The present application relates to methods for reducing the flammability of cellulosic substrates, including cotton fiber carpets and raised surface apparel.
Cotton, like most textile fibers, is combustible. Whenever cotton is in the presence of oxygen and the temperature is high enough to initiate combustion (360-420xc2x0 C.), untreated cotton will either burn (flaming combustion) or smolder (smolder combustion). The degree of flammability depends on the fabric construction. Fabrics have different flammability requirements depending on the particular end use. Cotton fabrics, without the use of special flame-retardant finishes, meet practically all of these requirements for most existing end-uses. However, some new cotton product developments require special constructions or finishes to reduce their flammability. This is especially true in certain countries, such as the United States, which have strict regulations governing the flammability of these products.
Resistance to burning is one of the most useful properties that can be imparted to cotton fibers and textiles. Some end uses for cotton in textiles for apparel, home furnishings, and industry, can depend on its ability to be treated with chemical agents (flame-retardants) that confer flame resistance (FR). End uses requiring flame-retardant finishes include protective clothing (e.g., foundry workers apparel and fire fighters uniforms), children""s sleepwear, furnishing/upholstery, bedding, carpets, curtains/drapes, and tents.
Chemical agents for reducing the flammability of products containing cotton fiber and other cellulosic fibers are well known and generally grouped into two categories: durable and non-durable. The durable type tend not to be removed in conventional washes and the non-durable type are typically removed in conventional washes.
The variable manufacturing cost of a typical durable flame-retardant treatment is about $1-2 per yard, depending on fabric weight and other factors. This can be a major limitation. The flammability and flame resistance of cotton has been studied extensively and several comprehensive reviews of the subject are available.
Cotton is not currently the raw material of choice in the carpet industry. The carpet fiber business in the U.S. is roughly a 7,000,000 bale/year market, and cotton is less than one percent of this overall market. One reason that cotton has been almost excluded from this large market for fibers is the difficulty in complying with the Flammable Fabrics Act. This regulation requires that all carpets which are six feet by four feet or larger and are sold for residential use pass a flammability test. This test is commonly referred to as the xe2x80x9cPill Testxe2x80x9d. It calls for igniting a methenamine pill, which is placed in the center of a nine-inch by nine-inch carpet specimen. The specimen fails if the flame spreads to within one inch of a metal template containing an eight-inch diameter hole, which is placed on top of the carpet specimen prior to igniting the pill. The specimen passes if the flame does not spread to within one inch of the metal template.
For a residential carpet to be saleable, at least seven out of eight specimens must pass the test. Furthermore, if the carpet has been treated with a flame-retardant (with the exception of alumina trihydrate added to the back coating), then the carpet must be washed ten times as described in AATCC 124-1967 prior to testing.
There are numerous man-made fiber carpets which are currently available, many of which do not require any special treatments to pass federal flammability requirements because of the nature of the test. Many synthetic carpet fibers will melt away from the burning pill during the pill test, such that the pill eventually self extinguishes. The fuel load provided by these carpets in a fire, which is already burning, is not considered by the test method.
Other synthetic fiber carpets, such as polypropylene, require a flame-retardant such as alumina trihydrate. Alumina trihydrate is often added to a backcoating (or backing), as opposed to application directly to the carpet fibers. Synthetic thermoplastic fibers such as polypropylene melt quickly when exposed to a flame, for example, during the pill test. The burning pill then quickly falls, due to gravity, onto the backing. The backing typically includes three layers: a thermoplastic (usually polypropylene) primary backing layer, a latex adhesive layer (which may contain the flame-retardant) and a secondary thermoplastic (usually polypropylene) backing layer. Since the primary backing is also a low melting point thermoplastic, it quickly melts and allows the burning pill to come into direct contact with the latex. Since the latex often includes a flame-retardant, it can then suppress the spread of flames.
Certain other fibers, such as wool and modacrylic, are inherently flame resistant. These can be made into carpets which require no special treatments to pass the required pill test. Cotton carpets can also be made which require no special treatments to pass the pill test. For example, a cut pile carpet can be made from a {fraction (3/2)} Ne yarn composed of 90 percent cotton and 10 percent low melt thermoplastic fiber. The low melt fiber is allowed to melt, typically prior to tufting of the carpet. A carpet which includes 12 stitches per inch, {fraction (1/11)}-inch gauge, and xc2xc inch pile height can be constructed from this yarn. Such a carpet is generally dense enough, with a sufficiently low pile height, that it will pass the pill test without any additional treatment.
A disadvantage of relying on such low pile height constructions when manufacturing cotton carpets is that it is very limiting from a design and marketing standpoint. The consumer in the U.S. today has become accustomed to a wide variety of choices when selecting a carpet. Substantially limiting the choices of carpet construction is not a practical option for a successful marketing program.
Another disadvantage of attempting to reduce the flammability of a cotton (or cellulosic) carpet by construction alone is that achieving reduced flammability often means increasing the area density (oz./square yard) of the carpet. As the area density of the carpet increases, the cost also generally increases. This approach is therefore very restrictive and would limit the market to the small, upper price end.
Alumina trihydrate, which is effective on certain thermoplastic fiber carpets, is not typically effective on cotton-containing carpets. On cotton-containing carpets, the cotton yarn which is under and in the vicinity of the burning pill will tend to char but maintain sufficient integrity to support, insulate and separate the burning pill from the carpet backing. There is not a sufficient heat flux reaching the alumina trihydrate contained in the latex backing for the alumina trihydrate to be effective at suppressing the flame.
The use of flame-retardant low melt fibers in place of the typical non-flame-retardant low melt fiber used in the yarn has been attempted. The low melt fiber, in general, offers the advantages of improved resilience and tuft definition and minimizes shedding of loose fibers from the tufts. Testing has shown that flame retardant low melt fiber used in the yarn is not effective. Although various explanations have been offered, the mechanism is not understood.
Since federal law in the U.S. requires that any carpet which has a flame-retardant treatment (other than alumina trihydrate) be laundered ten times prior to flammability testing, any such flame-retardant which is applied for that purpose must remain effective after the ten home launderings. Because home launderings are rather effective at removing materials which are not chemically bonded to the fibers, durable flame retardants are generally the most effective.
There have been many techniques for imparting durable flame resistance properties to cellulosic substrates described in the literature. However, there are relatively few that are practiced today, due to commercial availability of the chemicals, safety concerns, process control issues or other reasons. Durable flame retardants are typically more complex, more expensive and more difficult to apply than non-durable treatments. The main flame retardant finishes used on cotton are phosphorus-based.
Two of the more common phosphorous-based systems which are used to provide durable flame resistance to cotton substrates are the xe2x80x9cpre-condensatexe2x80x9d /ammonia process and the reactive phosphorous process.
In the xe2x80x9cpre-condensatexe2x80x9d/NH3 process, the flame-retardant agent exists as a polymer in the fibrils of cotton fibers and is not combined chemically with OH groups in the cotton fiber. This process imparts durable flame resistance to 100% cotton. fabrics when applied under proper application procedures. It produces fabrics with a good hand and strength retention. Proper application of pre-condensates to cotton fabrics requires adequate fabric preparation, proper padding/uniform application, proper phosphorus add-on relative to fabric properties, appropriate moisture control prior to ammoniation, control of the ammoniation step to ensure adequate polymer formation, and effective oxidation and washing of the treated fabric.
This process is very useful for specialty applications that can command a very high price, such as protective clothing for fire fighters and other workers who may be exposed to fire or excessive heat. It is generally not practical for cotton carpets or raised surface apparel that will be sold to the average consumer. The problems associated with this process include the high cost, the special equipment needed (ammoniation chamber) which is not generally available, and the two drying steps which are required.
Reactive phosphorus-based flame retardants are compounds (e.g., N-methylol dimethyl phosphonopropionamide (MDPPA)) that react with cellulose, the main constituent of cotton fiber. These compounds can be used both for cotton and for cotton blends with a low synthetic fiber content. The finish, usually applied to the fabric after the coloring stage, promotes char formation. The durability of the finish makes the resulting treated fabric suitable for curtains, upholstery, bed linen and protective clothing.
The reactive phosphorus-based flame retardants are typically applied using a pad/dry/cure method, in the presence of phosphoric acid catalyst. The finish is sometimes applied with a methylated melamine resin to increase the bonding/fixation of the agent to cellulose, which enhances the flame retardancy. Afterwashing is generally required, often with an alkali such as soda ash, followed by further rinsing and drying. The afterwashing helps to reduce loss of fabric strength. The reactive phosphorous-based process has the advantage of not requiring specialized equipment such as an ammonia cure unit, and has less affect on dyes than the pre-condensate process. However, this process can cause more strength loss than the pre-condensate process. Further, there can be a durability problem associated with some wash treatments if the instructions of the chemical supplier are not followed.
Reactive phosphorus based flame retardants can be unsuitable for certain end uses, such as cotton or cotton blend carpets. This is especially true when the products contain formaldehyde, because of concerns about the human health effects of exposure to certain volatile organic compounds (VOC""s) which may have been released from carpeting or carpet backing in past years. Because of this, most carpet manufacturers generally consider even very low levels of formaldehyde to be unacceptable. Another issue is that these products are generally designed to be afterwashed as part of the application procedure. While the toxicity of such materials is generally low, there are significant concerns about the exposure of babies or small children to residual unfixed chemicals left on the carpet.
Another phosphorous-based approach has been to apply a flame-retardant cyclic phosphonate ester and tetrakis-(hydroxymethyl)phosphonium sulfate (THPS) to polyester/cotton fabrics. The components are applied simultaneously and then cured (U.S. Pat. No. 4,842,609 to Johnson). The phosphonate ester bonds to the polyester, and the THPS bonds to the cotton fibers. The minimum amount of polyester when this composition is used is 35% by weight. The treated fabrics can purportedly be washed numerous times and also have an acceptable hand. A limitation of the chemistry is that it requires such a large percentage of polyester in the blend, and also that phosphorous compounds can be problematic, as discussed above. Other organophosphorous-based treatments include those described in U.S. Pat. No. 4,167,603 to Sistrunk, U.S. Pat. No. 3,897,584 to Swidler et al., U.S. Pat. No. 3,970,425 to Leblanc and LeBlanc, U.S. Pat. No. 4,040,780 to Garner, U.S. Pat. No. 3,650,820 to DiPietro et al., and U.S. Pat. No. 4,765,796 to Harper and Beninate.
A non-phosphorous approach for rendering cotton fire retardant has been to incorporate a water-insoluble, solid particulate mixture of brominated organic compounds and metal oxides, optionally with a metal hydrate, into the carpet fiber (U.S. Pat. No. 4,600,606 to Mischutin). However, a limitation of the chemistry is that the metal oxide compounds may be rendered soluble when washed if the pH of the solution is on the acid side. Also, particles of brominated organic compounds may be irritating to people coming into contact with them, and may be harmful if ingested.
Another non-phosphorous approach has been to prepare a solution of boric acid, ammonium sulfate, borax, hydrogen peroxide, and optionally a surfactant and/or an alkyl phthalate ester, and apply this as a coating on cellulosic materials. A major limitation of this chemistry is the water-solubility of the components, which results in the composition being substantially removed during conventional washing.
There is a need for fire retardants for cotton fiber, especially when the fiber is used in a cotton carpet or in raised surface apparel, that survives a certain number of washings, including steam cleanings. The present invention provides such materials.
Compositions and methods for providing cellulosic fibers with reduced flammability, and articles of manufacture prepared from the resulting fire-resistant cellulosic fibers, are disclosed,
The compositions include one or more amino acids, proteins and/or peptides, and optionally include one or more crosslinking and/or coupling agents. The methods involve applying to a cellulosic fiber a composition including an amino acid, protein and/or peptide, and optionally involve chemically combining the amino acid, protein and/or peptide to the hydroxy groups on the cellulosic fiber using crosslinking and/or coupling agents.
Suitable amino acids include naturally-occurring and synthetic amino acids. The amine group can be at a position alpha to the carboxylic acid group, or can be at positions other than or in addition to the alpha position. Many amino acids include reactive groups such as hydroxy groups, thiols, amines, and carboxylic acids. Carboxylic acids are known to react with hydroxy groups under various coupling conditions using known coupling agents to form ester linkages. Thiols, amines and hydroxy groups on amino acids, proteins and/or peptides do not react directly with the hydroxy groups on the cellulosic materials, but can be covalently linked via crosslinking agents. Preferred amino acids are those which are commercially available in large quantities, for example, lysine and arginine.
Proteins and peptides are prepared by forming peptide (amide) bonds between various amino acids. Suitable proteins include soy proteins, milk proteins such as casein, derivatives thereof, and enzymes. In a preferred embodiment, the protein is an enzyme. Suitable enzymes include cellulases, lipases, catalases, amylases, proteases, pectinases, xylanases, isomerases and beta-glucanases. Examples of suitable enzymes include the Denimax(copyright) family of enzymes sold by Novo Nordisk.
Cotton is a preferred cellulosic fiber. Other cellulosic fibers include flax, jute, hemp, ramie, lyocell and regenerated unsubstituted wood celluloses such as rayon.
The crosslinking agents are reactive molecules which include two or more leaving groups, such that a thiol, amine and/or hydroxy group on the amino acid, protein and/or peptide can react with one of the groups, and the other group can react with a hydroxy group on a cellulosic material. Examples of suitable crosslinking agents include dichlorotriazines, ureas, imidazolidinones, imidazoles, dialdehydes, urethanes, carbonates, orthocarbonates, chloroformate, dihalides such as 1,2-dichloroethane, diesters such as dimethylsuccinate, diacid halides such as succinyl chloride, and the like.
The carboxylic acids on the amino acids, proteins and/or peptides and the hydroxy groups on the cellulosic substrate can be linked via ester linkages with or without the use of coupling agents. In one embodiment, the esterification is performed using a catalyst and heat, using the esterification conditions disclosed in U.S. Pat. No. 4,820,307 to Welch et al., the contents of which are hereby incorporated by reference.
In another embodiment, more conventional esterification conditions, for example, forming acid halides and reacting the acid halides with the hydroxy groups on the cellulosic material in the presence of a tertiary amine, are used. This embodiment can be less preferred, due to the higher cost of the raw materials.
When the composition is applied to the cellulosic substrate by spray or foam, the percent by weight of the fire retardant solution which is applied to the cellulosic substrate is typically between about 5 and 100 percent by weight, preferably between about 10 and 50 percent by weight, and more preferably, between about 15 and 30 percent by weight of the fiber to be treated. These ranges vary depending on the mode of application and the cellulosic substrate to be treated. For example, for raised surface apparel, larger amounts of the fire retardant solution may be required to achieve adequate fire resistance. This same general principal, of adjusting the solution concentration based on the total wet add-on, applies to other substrates as well, such as fiber fill or upholstery.
The amino acids, proteins and/or peptides can also be applied by other application techniques including exhaust. In an exhaust application the liquor ratio may vary over a broad range of about 2 to 1 up to about 50 to 1. More preferably about 3 to 1 to about 20 to 1, meaning about 20 pounds of treating solution per pound of cellulosic containing substrate. In one preferred embodiment the liquor ratio is about 10 to 1 and the amino acid, protein and/or peptide concentration is adjusted accordingly down to a concentration ranging from 0.001 percent to about 5.0 percent and preferably from about 0.01 to 1.0 percent on the weight of the treating liquor which is equivalent to 0.1 percent to 10.0 percent on the weight of the cellulosic substrate. Wet coupling or crosslinking agents, which can also be applied by exhaust techniques from the same bath, can be applied with proteins, enzymes or amino acids to provide covalent linkages which result in treatments which are durable to various cleaning techniques. One such wet crosslinking agent is known as T-DAS, a dichlorotriazine.
The resulting cellulosic fiber is fire resistant. When the amino acid, protein and/or peptide is crosslinked with the cellulosic substrate, the linkages between the reactive groups on the amino acid, protein and/or peptide and the hydroxy groups on the cellulosic fiber are stable to most conventional washings, including the ten home launderings specified in 16 C.F.R. 1630 and 1631 for carpets which have been treated with a flame retardant.
The treated fiber can be present alone or as blends of cotton and other commercially available fibers, including polyester. The fibers can be used to prepare suitable articles of manufacture, including carpets, raised surface apparel, other garments, upholstery, and other articles which have acceptable fire resistance based on required tests for that particular use. In a preferred embodiment, the fiber is cotton and the article of manufacture is a cotton-based carpet or raised surface apparel. The treated cotton carpets can have an area density between about 20 oz/yd2 and 120 oz/yd2, preferably between about 30 oz/yd2 and 80 oz/yd2.
The compositions can optionally include additional components, such as other fire retardants, dyes, wrinkle resist agents, foaming agents, buffers, pH stabilizers, fixing agents, stain repellants such as fluorocarbons, stain blocking agents, soil repellants, wetting agents, softeners, water repellants, stain release agents, optical brighteners, emulsifiers, and surfactants.